It is known to add passivants to plasma etch chemistries to induce anisotropy. Typical passivants generate unsaturated radicals (e.g., CFx, CClx, CHx, etc.) in the plasma that oligomerize to form sidewall films that inhibit lateral etching. While previous examples are based on carbon based polymerizing chemistries; inorganic passivants have also been employed (e.g., Si containing, B containing, S containing, etc.).
Etchant-unsaturate (Etchant-passivant) strategies are used extensively in plasma processing. The etchant is typically a halogen and the unsaturate is typically carbon based in order to maintain an anisotropic etch, a balance must be achieved between the etchant and the passivant. If the balance is skewed by too much etchant, then the process becomes more isotropic inducing mask undercut which results in critical dimension (CD) loss. If the balance is skewed by too much passivant, then a passivation film may form on the surfaces to be etched, thereby stopping the etch.
In order to achieve a balance between the etch and passivation mechanisms, a third component may be added to the process gas mixture. In the case where the passivant is polymer based, an oxidant (e.g., oxygen containing compound) or reducer (e.g., hydrogen containing compound) may be added to the system. In this case, oxidant addition favors the etchant and reduces passivation efficiency while reducer (e.g., hydrogen) addition favors passivation formation. An example of this approach is the plasma etching of SiO2 in fluorocarbon chemistries with the addition of hydrogen (for more passivation) or an oxidant (for less passivation).
In some cases it is disadvantageous to directly mix the passivant and etchant. By way of example, it is well known that Si etches isotropically in free fluorine. Adding unsaturated fluorocarbons to the process as a passivant to remain anisotropy consumes free fluorine resulting in reduced Si etch rates—furthermore, the free fluorine etchant also reduces the passivation efficiency. One solution to this limitation is time division multiplexed (TDM) etching. In this case the etchant and passivant are separated in time. The process is converted from a continuous etch process into a series of loops. Each loop typically consists of a passivation step to protect the etch sidewall, an anisotropic break through step to remove passivation from horizontal surfaces, and a main etch step; which is typically at least partially isotropic. The loops are then repeated in a cyclical fashion. For silicon etching, examples of this process are described in U.S. Pat. No. 5,501,893 and U.S. Pat. No. 4,985,114.
Dry etch processes are being more frequently used in the fabrication of photolithographic reticles 110. In the case of fabricating a binary chrome photomask, a pattern is defined into an etch mask 100 (e.g. photoresist which is typically by optical or electron beam lithography). A plasma etch process is then used to transfer the pattern of the etch mask 100 into the underlying film 105 (see FIG. 1). Ideally the CD of the initial etch mask 115 is replicated exactly into the final etch feature CD 125. Typically however, there is often a difference in the CD of the initial mask image 115 and the CD of the final etch pattern 125. This difference is typically referred to as the CD bias of the process 120. Plasma etching of chrome (Cr) containing films is typically performed in a Cl2/O2 based chemistry producing CrO2Cl2 (chromyl chloride) as a volatile by product. Typically, the oxygen composition of the process gas mixture is between approximately 5% and 30% resulting in a Cr etch that has some degree of anisotropy. The presence of oxygen in the process gas mixture tends to promote etching of organic materials such as photoresist. This etching of the resist is not entirely anisotropic and may result in some lateral etching of the patterned features resulting in a CD change. Higher oxygen concentrations tend to further reduce photoresist (PR:Cr) etch selectivity, and ultimately may induce undercutting of the Cr; both of these mechanisms tend to increase CD bias. Due to the presence of oxygen, plasma chrome etching has historically not been performed using a etchant-passivation strategy where the passivant is polymer based. Polymer addition in the presence of oxygen tends to consume the oxygen (e.g., forming CO, CO2, H2O, etc.) which compromises both the etch and passivation efficiency.
Some groups have attempted different passivation schemes for use in conjunction with a Cl2/O2 plasma based Cr etch processes. For example, it is known in the art to add COx, SOx, and HCl in efforts to promote passivation and improve the Cr etch process.
Based on the limitations of the prior art, there is a need for an improved method of etching material from a photolithographic reticle in a manner that reduces process induced CD bias.
Nothing in the prior art provides the benefits attendant with the present invention.
Therefore, it is an object of the present invention to provide an improvement which overcomes the inadequacies of the prior art devices and which is a significant contribution to the advancement to the processing of photomasks and reticles.
Another object of the present invention is to provide a method for improving the critical dimension performance during a plasma etching process of a photolithographic substrate having a thin film, comprising: depositing a passivation film on said photolithographic substrate using a first set of process conditions; etching said deposited film from said photolithographic substrate using a second set of process conditions; etching an exposed surface of said photolithographic substrate using a third set of process conditions; and monitoring the critical dimension performance of said photolithographic substrate.
Yet another object of the present invention is to provide a method for improving the critical dimension performance during a plasma etching process of a photolithographic substrate having a thin film, comprising: predetermining the critical dimension performance of a deposition process; predetermining the critical dimension performance of a first etch process; predetermining the critical dimension performance of a second etch process; selecting a first set of process conditions based on said predetermined critical dimension performance of said deposition process step; depositing a passivation film on the photolithographic substrate using said first set of process conditions; selecting a second set of process conditions based on said predetermined critical dimension performance of said first etch process step; etching said deposited film from the photolithographic substrate using said second set of process conditions; selecting a third set of process conditions based on said predetermined critical dimension performance of said second etch process step; and etching an exposed surface of the photolithographic substrate using said third set of process conditions.
Still yet another object of the present invention is to provide a method for improving the critical dimension performance during a plasma etching process of a photolithographic substrate having a thin films comprising: depositing a passivation film on said photolithographic substrate using a first set of process conditions; etching said deposited film from said photolithographic substrate using a second set of process conditions: and etching an exposed surface of said photolithographic substrate using a third set of process conditions.
The foregoing has outlined some of the pertinent objects of the present invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.